System, method and apparatus for plasma etch having independent control of ion generation and dissociation of process gas

ABSTRACT

A method of etching a wafer includes injecting a source gas mixture into a process chamber. The injecting includes injecting the source gas into multiple hollow cathode cavities in a top electrode, generating plasma in each of the cavities, and outputting the plasma from corresponding outlets of the cavities into a wafer processing region in the chamber, where the processing region is located between the outlets and a surface to be etched. An etchant gas mixture is injected into the processing region through injection ports in the top electrode such that the etchant gas mixes with the plasma output from the outlets. The etchant gas is prevented from flowing into the outlets of the cavities by the plasma flowing from the outlets. Mixing the etchant gas and the output from the cavities generates a desired chemical species in the processing region and thereby enables the surface to be etched.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/713,523, filed Feb. 26, 2010, the disclosure of which is incorporatedherein by reference in its entirety for all purposes.

BACKGROUND

The present invention relates generally to plasma etch systems andmethods, and more particularly, to systems and methods for plasma etchhaving independent control of ion generation and dissociation of processgas.

A simplified description of a typical plasma etching process is plasmachamber with a process gas therein. The process is excited by an RF ormicrowave signal electrically coupled into the process gas. Exciting theprocess gas causes ions and radicals to form within the process gas. Theions and radicals are then directed toward a surface to be etched. Theions and radicals can be directed toward the surface to be etched usinggas flows and electrical biasing of various surfaces within the plasmachamber. The ions and radicals react with the material in the surface tobe etched.

Increasing a density of an etching plasma is one method to increase howfast the etch surface is etched (e.g., etch rate, usually expressed inAngstroms per minute). Increasing the density of an etching plasmaincreases the concentration of the ions and thus increases thereactivity between the process gas, ions and the etch surface. However,increasing plasma density can also cause excess dissociation of theprocess gas mixture into constituent elements or molecules, beyond thelevel of dissociation which is optimal.

For example, increased plasma density typically causes atomic fluorineradicals to dissociate from a fluorocarbon process gas mixture. Thedissociated fluorine may accelerate the undesirable etch of the etchmask, of the feature sidewall, or of the etch stop layer underlying thelayer to be etched. Additionally, the excessive dissociation offluorocarbon source gas may lead to non-optimal composition offluorocarbon radical species in the plasma, with effects similar toexcessive fluorine.

There are other issues of uniformity and control that are also reducedor less than desirable that can occur when the process gas isdissociated too much. In view of the foregoing, there is a need forsystems and methods for plasma etch having independent control of iongeneration and dissociation of process gas.

SUMMARY

Broadly speaking, the present invention fills these needs by providingsystems and methods for plasma etch having independent control of iongeneration and dissociation of process gas. It should be appreciatedthat the present invention can be implemented in numerous ways,including as a process, an apparatus, a system, computer readable media,or a device. Several inventive embodiments of the present invention aredescribed below.

One embodiment provides a method of etching a semiconductor waferincluding injecting a source gas mixture into a process chamberincluding injecting the source gas mixture into a multiple hollowcathode cavities in a top electrode of the process chamber andgenerating a plasma in each one of the hollow cathode cavities.Generating the plasma in the hollow cathode cavities includes applying afirst biasing signal to the hollow cathode cavities. The generatedplasma is output from corresponding outlets of each of the hollowcathode cavities into a wafer processing region in the process chamber.The wafer processing region is located between the outlets of the hollowcathode cavities and a surface to be etched. An etchant gas mixture isinjected into the wafer processing region. The etchant gas mixture isinjected through multiple injection ports in the top electrode such thatthe etchant gas mixture mixes with the plasma output from the outlets ofthe hollow cathode cavities. The etchant gas mixture is substantiallyprevented from flowing into the outlets of the hollow cathode cavitiesby the plasma and source gas mixture flowing from the outlets of hollowcathode cavities. Mixing the etchant gas mixture and the plasmagenerates a set of desired chemical species in the wafer processingregion, leading to optimal etch results at the surface to be etched.

Generating plasma in each one of the hollow cathode cavities can includecooling the top electrode. Biasing the hollow cathode cavities caninclude applying the first biasing signal to a second conductive layerof the top electrode, the hollow cathode cavities being formed in thesecond conductive layer. The first biasing signal can include an RFbiasing signal. The first biasing signal can include an RF signal withina range of between about 1 MHz and about 15 MHz.

The multiple injection ports can be substantially distributed across thewafer processing region surface of the top electrode. The hollow cathodecavities can be substantially distributed across the wafer processingregion surface of the top electrode. The multiple hollow cathodecavities and the multiple injection ports can be substantially evenlyinterspersed across the wafer processing region surface of the topelectrode.

Outputting the generated plasma from corresponding outlets of each ofthe hollow cathode cavities can include applying a second biasing signalto the lower electrode. Generating plasma in each one of the hollowcathode cavities can include applying a third bias signal to the outletsof the hollow cathode cavities. The third bias signal can be a groundpotential.

Etching the surface to be etched can include applying a fourth biassignal to the wafer-supporting electrode or to another electrode coupledto the wafer processing region, to augment the plasma generation andwafer ion bombardment provided by the plasma flowing from the hollowcathode cavities.

Etching the surface to be etched can include removing etch byproductsfrom the wafer processing region. A ground potential can also be appliedto a first conductive layer of the top electrode. The hollow cathodecavities can include multiple hollow cathode trenches. The multipleinjection ports in the top electrode can include a multiple injectiontrenches. The source gas mixture can be an inert gas. The etchant gasmixture can include a fluorocarbon containing gas. The outlet for eachone of the hollow cathode cavities can have width more than twice aplasma sheath thickness.

Another embodiment provides a system for generating an etching speciesincluding a source gas mixture source, an etchant gas source and aprocess chamber. The process chamber includes a top electrode and abottom electrode. The top electrode includes multiple hollow cathodecavities, with the source gas mixture source coupled to an inlet of eachone of the hollow cathode cavities. The top electrode also includes afirst biasing signal source coupled to each one of the hollow cathodecavities and a corresponding outlet for each one of the hollow cathodecavities. The corresponding outlets open to a wafer processing region inthe process chamber. The wafer processing region being located betweenthe outlets of each of the hollow cathode cavities and a surface to beetched. The top electrode also includes multiple injection ports coupledto the etchant gas source. The injection ports are capable of injectingthe etchant gas into the wafer processing region. The bottom electrodecan support a semiconductor wafer, the semiconductor wafer including thesurface to be etched.

Each one of the corresponding outlets can have a width greater thantwice a plasma sheath thickness. Alternatively, each one of thecorresponding outlets can have a width less than or equal to twice aplasma sheath thickness.

Another embodiment provides a method of etching a semiconductor waferincluding injecting a source gas mixture into a process chamberincluding injecting the source gas mixture into multiple hollow cathodecavities in a top electrode of the process chamber, generating a plasmain each one of the hollow cathode cavities including applying a firstbiasing signal to the plurality of hollow cathode cavities, producingactivated species in the hollow cathode cavities and outputting theproduced activated species from corresponding outlets of each of thehollow cathode cavities into a wafer processing region in the processchamber. The wafer processing region being located between the outletsof each of the hollow cathode cavities and a surface to be etched. Anetchant gas mixture is injected into the wafer processing region. Aplasma is produced in the wafer processing region by coupling a secondbiasing signal to the wafer-supporting electrode or another electrodewhich is electrically coupled to the wafer processing region. Theetchant gas mixture being injected through one or more injection portsin the top electrode such that the etchant gas mixture mixes with theactivated species output from the outlets of the hollow cathode cavitiesand including generating a desired chemical species in the waferprocessing region . The etchant gas mixture is substantially preventedfrom flowing into the outlets of each of the hollow cathode cavities bythe activated species flowing from the outlets of each of the hollowcathode cavities. The outlet for each one of the hollow cathode cavitieshas a width of less than twice a plasma sheath thickness. The surface tobe etched is then etched.

Other aspects and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of a plasma processing chamber systemhaving multiple hollow cathode plasma cavities in the upper electrode,in accordance with embodiments of the present invention.

FIG. 2 is a more detailed view of a single one of multiple hollowcathode plasma cavities, in accordance with embodiments of thepresenting invention.

FIG. 3 is a schematic diagram of a two dimensional array of DC orRF-powered hollow cathode (HC) cavities in an upper electrode, inaccordance with embodiments of the present invention.

FIG. 4 is a schematic diagram of a two dimensional array of DC orRF-powered hollow cathode trenches in an upper electrode, in accordancewith embodiments of the present invention.

FIG. 5 is a flowchart diagram that illustrates the method operationsperformed in generating an increased plasma density without increaseddissociation, in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION

Several exemplary embodiments for systems and methods for plasma etchhaving independent control of ion generation and dissociation of processgas will now be described. It will be apparent to those skilled in theart that the present invention may be practiced without some or all ofthe specific details set forth herein.

Typical plasma chambers for etching dielectric wafer films have a commonproblem. Etch rate of the targeted material is often limited by the ionflux reaching the surface. To obtain higher etch rates, and thus a moreefficient etch process, ion flux can be increased. As process controlparameters are adjusted to produce relatively high ion flux to the wafersurface to be etched, the corresponding increase in plasma density leadsto an increase in dissociation of the process gas(es). This changes thecombination of chemical species present in the plasma. Morespecifically, the same parameter changes that increase the ion flux tothe wafer generally also increase the electron density of the plasma.The electron density is a plasma condition which directly influencesrates of molecular dissociation of the process gas(es) chemistry in theplasma, and thereby changes the chemical composition of the plasma(e.g., ratios between different radicals, process gas parent molecules,and etch byproducts). There is more dissociation as the plasma densityincreases causing corresponding changes in the overall plasma chemistry.

Fluorocarbon (or hydrofluorocarbon) source gases (FC gases) aretypically used to etch SiO2, SiNx, SiOCHx, and other silicon-baseddielectrics. Excessive dissociation leads to unfavorable plasmaconditions and less than optimal process results. Specifically, too muchdissociation creates a plasma chemistry that is too “lean”, meaning thetendency to etch surfaces is too strong and the tendency to passivatesurfaces by forming fluorocarbon (FC) thin films is too weak. Too muchdissociation converts polymerizing neutral species such as CxFy (X=2, 3,4) to etching neutral species such as CFx (X=1, 2, 3) and F resulting inreduced polymerization of the source gases on surfaces. The excessdissociation and the resulting low polymerization of the source gasescauses low etch selectivity to mask and substrate films, as well asundesirable sidewall etching.

Adjusting the gas mixture in the plasma chemistry can sometimes at leastpartially compensate the excess dissociation. However, adjusting the gasmixture cannot completely overcome the low polymerization limitations ofthe high density plasma. An extreme example of this problem is seen whenhigh-density inductively couple plasma (ICP) sources are used with FCgases. The result is a low selectivity to organic mask materials.

The close coupling between ion flux and electron density makes itdifficult to obtain a plasma condition which combines a high ion fluxand an optimal fluorocarbon plasma chemistry. This close coupling forcesa tradeoff between a high etch rate and a high selectivity. Thistradeoff is commonly encountered in high-aspect-ratio (HAR) contact orcell etching, where high etch rates are desirable due to the relativelythick films, and high selectivity is desired due to the cost andcomplexity of supplying thick mask films.

One approach to providing an increased plasma density without increaseddissociation is to create a high density plasma but with a lowerelectron temperature as compared to typical conditions for HARdielectric etch. This allows high ion fluxes to reach the wafer surface,but reduces the fraction of electrons with sufficient energy to inducedissociation of process gas. This can be achieved by spatiallyseparating the plasma activation or generation from the process gasdissociation, in a way that allows uniform injection of both plasma andprocess gas into the wafer processing region. In this way, the plasmainteracting with the substrate to be processed will have the benefit oflow dissociation but high plasma density, because the plasma isgenerated or alternatively gases are preactivated in a region which isseparated from the process gases.

One approach to increase plasma density without increase dissociationincludes directly injecting plasma from the plasma source to the waferprocessing region. The plasma density in the wafer processing region isprovided and/or augmented by the injected plasma, such that the electrontemperature and thus the process gas dissociation rate is not increased.

Another approach to increase plasma density without increasedissociation includes injecting activated species from the plasma sourceto the wafer region. These species may include metastable electronicallyexcited atoms and molecules, vibrationally excited molecules, orradicals produced by molecular dissociation, such that these specieshave a substantially lower ionization energy than the parent atoms andmolecules present in the source gas mixture. Plasma is produced in thewafer processing region by an electrical excitation which is distinctfrom the excitation of the plasma source. By way of example the lowerelectrode 104 can have an RF biasing signal S2 applied (e.g., 27 MHz)and the third conductive layer 112 of the top electrode can have aground potential S3 applied. A portion of the activated species will beionized by the plasma in the wafer processing region. Due to the reducedionization potentials which characterize the activated species, relativeto the unactivated source gas mixture, plasma equilibrium will beachieved with lowered electron energies, and therefore the plasma in thewafer processing region will adjust to a lower electron temperature.This lowered electron temperature will tend to produce less dissociationof the etchant gas mixture at the same plasma density, or samedissociation at higher plasma density. In both cases, the augmentationof the plasma density in the wafer processing region can be controlledby the power supplied to the plasma source(s), largely decoupled fromthe dissociation rate of process gas in the wafer processing region.

FIG. 1 is a schematic diagram of a plasma processing chamber system 100having multiple hollow cathode plasma cavities 108 in the upperelectrode 103, in accordance with embodiments of the present invention.FIG. 2 is a more detailed view of a single one of multiple hollowcathode plasma cavities 108, in accordance with embodiments of thepresenting invention. The system 100 includes a plasma processingchamber 101 and a controller 125. The plasma processing chamber 101includes the upper electrode 103 and the lower electrode 104. The lowerelectrode 104 includes a chuck which supports and is electricallycoupled to the wafer 102. The plasma processing chamber 101 alsoincludes a wafer processing region 106 between the upper electrode 103and the lower electrode 104. The wafer processing region can have a gapD11 of between about 16 mm and about 36 mm.

Multiple gas sources 129, 141 are coupled to the plasma processingchamber 101. Two gas sources 129, 141 are shown however more than twogas sources could also be included in or coupled to the system 100. Thegas sources 129, 141 also include subsystems for controlling gasflowrate and mixing (e.g., valves, manifolds, flow monitors and flowcontrollers). The gas sources 129, 141 also include subsystems forcontrolling gas pressure the gases contained therein.

Multiple biasing (RF and/or DC) signal sources S1-S5 are also includedin the system 100. The biasing signal sources S1-S5 are coupled toportions of the upper electrode 103 and lower electrode 104 as will bedescribed in more detail below.

The upper electrode 103 includes a temperature control system 122A forcontrolling the temperature of the upper electrode. The upper electrode103 also includes multiple hollow cathode plasma cavities 108. The upperelectrode 103 also includes delivery plenums 124 and 126 fordistributing the respective gases 128, 140 from the respective gassources 129, 141 to respective points of use as described in more detailbelow.

The upper electrode 103 can be formed in multiple layers. By way ofexample a temperature control layer 122 can be a good thermal conductivematerial such as a metal (aluminum, stainless steel, other suitablethermally conductive material or combinations of materials), siliconcarbide. The temperature control layer 122 has a thickness D10 of anysuitable dimension. Byway of example thickness D10 can be between lessthan about 3 mm and more than about 100 mm.

A first conductive layer 120 can be formed above the HC cavities 108.The first conductive layer 120 can be biased to assist in directing theplasma 140A formed in the HC cavities 108 as described in more detailbelow. The first conductive layer 120 has a thickness D9 of betweenabout 3 mm and about 10 mm. An electrically insulating layer (not shown)can optionally be included between the temperature control layer 122 andthe first conductive layer 120.

A second conductive layer 116 includes the HC cavities 108. As will bedescribed in more detail below, forming the HC cavities 108 in aconductive layer allows a relatively simple structure for applying abiasing signal Si to the HC cavities. A first insulating layer 118electrically isolates the second conductive layer 116 from the firstconductive layer 120. The first insulating layer 118 has a thickness D8of between about 1 mm and about 6 mm.

A second insulating layer 114 electrically isolates the secondconductive layer 116 from a third conductive layer 112. The secondinsulating layer 114 has a thickness D7 of between about 1 mm and about6 mm. The third conductive layer 112 can be biased to assist indirecting the plasma 140A formed in the HC cavities 108 as described inmore detail below. The third conductive layer 112 has a thickness D6 ofbetween about 3 mm and about 10 mm.

The controller 125 includes controller sub-systems including logic,software, processor(s), hardware, input/output subsystems, displaysubsystems, data storage systems, memory systems, communications andnetworking subsystems. The controller 125 includes a recipe that definesthe desired operation of the plasma chamber system 100. The controller125 is coupled to various sensor systems (e.g., electrical, optical,pressure, temperature, etc.) in the plasma processing system 100 tomonitor the processing within the plasma processing system. Thecontroller 125 is also coupled to control inputs and/or feedback outputsof the biasing signal sources S1-S5, the gas sources 129, 141,temperature control system 122A and to various actuators for moving(e.g., raising lowering, lateral movement, opening-closing, etc.)various components and, in some embodiment, the wafer 102 in the plasmaprocessing system 100.

FIG. 3 is a schematic diagram of a two dimensional array of DC orRF-powered hollow cathode (HC) cavities in an upper electrode 103, inaccordance with embodiments of the present invention. FIG. 4 is aschematic diagram of a two dimensional array of DC or RF-powered hollowcathode trenches in an upper electrode 103, in accordance withembodiments of the present invention. FIGS. 1, 2 and 3 show multiplediscrete HCs 108 and discrete injection ports 127 in the surface of theupper electrode 103. The embodiment shown in FIG. 4 replaces at leastsome of the discrete HCs 108 and discrete injection ports 127 withtrenches 108′ and 127′, respectively, in the surface of the upperelectrode 103. The trenches 108′ and 127′ can simplify manufacturing andassembly. It should be understood that the embodiments are shown insimplified, schematic form and are not necessarily drawn to scale.

The HC cavities 108 generate plasma via a hollow cathode effect wherehigh energy electrons are trapped between the cathode walls. The HCcavity 108 has a width D4 of between about 3 mm and about 25 mm. The HCcavity 108 has a height D5 of between about 3 mm and about 25 mm.

The discrete HCs 108, discrete injection ports 127, and trenches 108′and 127′ are shown substantially evenly distributed across the surfaceof the upper electrode 103. However, it should be understood that thedistribution of the discrete HCs 108, discrete injection ports 127, andtrenches 108′ and 127′ may not be as evenly distributed as shown. Itshould also be understood that the relative sizes of the discrete HCs108, discrete injection ports 127, and trenches 108′ and 127′ may not beas illustrated in FIGS. 1-4.

FIG. 5 is a flowchart diagram that illustrates the method operations 500performed in generating an increased plasma density without increaseddissociation, in accordance with one embodiment of the presentinvention. The operations illustrated herein are by way of example, asit should be understood that some operations may have sub-operations andin other instances, certain operations described herein may not beincluded in the illustrated operations. With this in mind, the methodand operations 500 will now be described.

In an operation 505, the HC cavities 108 and/or trenches are suppliedwith a source gas 140 via distribution plenums 126. In an operation 510,a first signal Si is applied to the HC cavities 108 to generate a plasma140A and/or activated species therein. A high density plasma 140A can beproduced at moderate pressures of between about 20 to about 5000 mT andmore particularly at a pressure of between about 50 and 1000 mT. In anoperation 515, the plasma 140A and/or activated species is deliveredinto a wafer processing region 106 located between the surface 102A tobe etched and outlets 108A of the HC cavities 108.

The source gas 140 is supplied from the top of the HC cavities 108 toprovide an optimal pressure in the HC cavities. The source gas 140 canbe a pure gas or gas mixture of two or more gases. The source gas 140 issubstantially inert and not reactive with the surface to be etched. Byway of example the source gas(es) 140 can include one or a mixture ofargon, xenon, or even a molecular gas such as N2 or O2. Although N2 andO2 are not normally considered inert, source gas may be considered asinert in this instance if the source gas, N2 and O2 and any dissociationthereof do not cause appreciable modification to the inner surfaces ofthe HC cavity 108 or trench, and do not include gases such asfluorocarbon gases which are intended to have low levels ofdissociation.

Where activated species are injected into the wafer processing region106, the source gas is selected to produce such desired species. Forexample, rare gas atoms such as argon and xenon are known to producemetastable electronically excited atoms under typical plasma conditions.These metastable atoms may have much lower ionization potentials thanthe ground-state atom. Likewise the N2 molecule is also relativelyefficient at populating metastable electronic states under typicalplasma conditions. As another example, CO molecule may also bebeneficial, as it can dissociate in the source region to produce atomicC radicals which have a lower ionization potential than the CO molecule.

A fluorocarbon or other halide-containing etchant gas 128 is notconsidered inert, as may etch or form deposits on the inner surfaces ofthe HC cavity 108 and the surface 102A to be etched. A dissociation of afluorocarbon or other halide-containing etchant gas 128 can alsostrongly affect etch results as described above. Therefore, thefluorocarbon or other halide-containing etchant gas 128 is not injectedthrough the HC cavity 108. However, a fluorocarbon or otherhalide-containing etchant gas 128 is still needed for theetching/chemical reaction with the surface 102A to be etched.

The fluorocarbon or other halide-containing etchant gas 128 can alsoinclude a mixture of gases. Some gases in the etchant gas mixture may beinert and some gases in the mixture may be reactive. The ratios of thegases in the etchant gas mixture may be adjusted to achieve a desiredratio. Etchant gas 128 can be a single gas or a gas mixture whichcontains the chemical species or precursors thereof which act aschemical etchant at the surface to be etched 102A. By way of example,the etchant gas 128 can include fluorocarbons for SiO2 etch or C12 forSi etch. Other gases such as O2, CH4, or HBr may be mixed with thefluorocarbon containing gas(es), to provide sidewall passivation orother beneficial effects.

In an operation 520, a second gas including the fluorocarbon or otherhalide-containing etchant gas 128 is injected into the wafer processingregion 106. The second gas bypasses the HC cavities 108 and is injecteddirectly into the wafer processing region 106 via injection ports 127.The injection ports 127 are located between the outlets 108A of the HCcavities 108. Injecting the etchant gas 128 can include delivering theetchant gas from an etchant gas source 129 to one or more deliveryplenums 124. The delivery plenums 124 distribute the etchant gas 128 tothe injection ports 127. The etchant gas 108 is injected into the waferprocessing region 106 from the injection ports 127. Thus, thefluorocarbon or other halide-containing etchant gas 128 bypasses the HCcavities 108 and is injected directly into the wafer processing region106.

In an operation 530, the etchant gas 128 mixes with the plasma 140Aand/or activated species output from the HC outlets 108A in the waferprocessing region 106. When activated species are output from the HCoutlets 108A, a plasma can be generated in the wafer processing region106 bay applying a biasing signal S2 to the lower electrode 104 and aground potential signal S3 to the third conductive layer 112 of theupper electrode. A combination of a selected flow rate of the source gas140 and width D2 of the outlets 108A and vertical length D6+D7 of theoutlets 108A determine a pressure drop as the plasma 140A and/oractivated species flows from the outlet 108A of the HCs 108. Outlets108A width D2 can be between about 1.0 mm and about 15 mm and theoutlets 108A length D6+D7 can be between about 1.0 mm and about 12 mm.For gas flow through an aperture, the ratio of the net flow rate to thearea represents the flux, and this parameter can be adjusted todetermine the ability of the net gas flow to prevent undesirable gastransport in the opposite direction. The flux of gas 140 and plasma 140Athrough the outlets 108A substantially prevents gas species present inthe wafer processing region 106 from entering the HCs 108 through theopenings 108A. Thus, the etchant gas 128 and its dissociation andreaction products are substantially prevented from interacting with thesurfaces inside HCs 108.

A combination of a selected flow rate of the source gas 140 and width D3of the port(s) 140B and vertical length D12 of the port(s) 140Bdetermine a pressure drop as the gas 140 flows into the HCs 108. Theflux of gas 140 through the port(s) 140B and the width D3 substantiallyprevent plasma from extending into the source gas supply plenum 126.Port(s) 140B have a width D3 that is nominally less than about 2 x theplasma sheath thickness. By way of example the width D3 can be betweenabout 0.1 mm and about 0.7 mm. The aperture(s) 140B length D12 can bebetween about 1 mm and about 12 mm.

A combination of selected flow rate of the etchant gas 128 and width D1and length D13 of the apertures 127B determine the pressure drop of theetchant gas 128 into the wafer processing region 106. Aperture 127Bwidth D1 can be between about 0.3 mm and about 0.8 mm and the aperturelength D13 can be between about 2.0 mm and about 20.0 mm. The flux ofthe etchant gas 128 and the width D1 of the apertures 127B substantiallyprevents gas species present in the wafer processing region 106 fromentering the injection ports 127. The ratio of flow rates of the sourcegas 140 and the etchant gas 128 can be selectively controlled such as byvarying the pressures of the respective gas sources 129, 141.

By way of example, the ratio of flow rates of the source gas 140 and theetchant gas 128 can be selectively controlled so that a larger portionof the total gas flow into the wafer processing region 106 is the sourcegas 140 and plasma ions 140A outlet from the HCs 108. Similarly, theratio of flow rates of the source gas 140 and the etchant gas 128 can beselectively controlled so that a larger portion of the total gas flowinto the wafer processing region 106 is outlet from the injection ports127. Also similarly, the ratio of flow rates of the source gas 140 andthe etchant gas 128 can be selectively controlled so that the total gasflow into the wafer processing region 106 is divided substantiallyevenly between the etchant gas 128 outlet from the injection ports 127and the source gas 140 and plasma ions 140A outlet from the HCs 108.

The width D2 of the openings 108A of the HC cavities 108 substantiallyprevent the etchant gas 128 from flowing from the wafer processingregion 106 and into the HC cavities. The width D2 is determined by achoice of plasma and/or activated species is desired to be output fromthe HCs 108, and by dynamics of the particular plasma 140A. By way ofexample, the width D2 is wider than twice a plasma sheath thickness soas to make sure the plasma is transported through the openings 108A andinto the wafer processing region 106. Conversely, if only activatedspecies and not plasma 140A is intended to be injected into the waferprocessing region 106, then the width D2 would be made smaller thantwice a plasma sheath thickness to ensure the plasma is extinguished inthe openings 108A.

The HCs 108 and/or trenches 108′ are distributed across the face of theupper electrode 103 so as to deliver a substantially uniform flow andmixture 208 of the etchant gas 127 and the plasma ions 140A across thewafer processing region 106 and to the surface 102A to be etched. In anoperation 540, the electrons of the plasma 140A interact with theetchant gases 127, in the wafer processing region 106, to inducecontrolled dissociation and create the desired chemical species 208needed for the etch reaction and associated passivation with the surface102A. Due to remote nature of the plasma source(s) 108 and the diffusionof plasma 140A from the HCs 108 into the wafer processing region 106, ordue to the transport of activated species with lowered ionizationpotentials from the HCs 108 into the wafer processing region 106, theelectron temperature in the wafer processing region is significantlylower than the typical electron temperature currently typical for HARdielectric etch.

In an operation 550, a portion of the plasma 140A and the desiredchemical species 208 is delivered to the surface 102A to be etched whichetches the surface to be etched. Etching the surface 102A generates etchbyproducts. In an operation 560, the etch byproducts are removed fromthe wafer processing region 106. Delivering the plasma 140A and thedesired chemical species 208 to the surface 102A to be etched alsoincludes applying a signal from signal source S2 to the lower electrode104. The signal S2 can be an RF bias to control ion bombardment energy.RF bias has a well known advantage over DC bias, RF bias can be appliedthrough dielectric films with minimal potential drop (e.g. oxide filmson the wafer surface or ceramic layers in the ESC). It should beunderstood that the signal S2 can include both RF and DC signals to biasthe lower electrode 104. The bias signal S2 applied to lower electrode104 may also produce and/or augment a plasma density in the waferprocessing region 106.

Bias signals S3 and S4 can be provided to the respective top 120 andbottom 112 of the HC cavities 108 to improve the delivery of the plasma140A from the HC cavities. The bias signals S3 and S4 can be a groundpotential. The temperature control layer 122 can be biased with the samebiasing signal S4 as the first conductive layer 120. Alternatively andas described above, an optional insulating layer can electricallyisolate the temperature control layer 122 from the first conductivelayer 120, thus allowing the temperature control layer to be biased withsignal S5 that is different from the bias signal S4 applied to the firstconductive layer.

The source gas 140 is injected into the top of the HC cavities 108through one or more ports 140B having a width D3. The multiple smallports 140B substantially prevent the plasma 140A from leaking upwardfrom the HC cavities 108 and into the delivery plenums 126. Conversely,the plasma injection at the outlet 108A of the HCs 108 is a singleopening to allow plasma transport and/or active species transport withthe minimum possible gas conductance.

In an exemplary embodiment, the signal S1 would be an RF in the 1-15 MHzrange to avoid possible problems with DC-floating surface films on theelectrode surfaces. The source gas 140 would be Argon and the etchantgas 128 would be a mixture of fluorocarbons, hydrofluorocarbons, and/or02.

There are many alternative embodiments possible. By way of example, thecathode and ground signals S1, S3, S4 of the HC cavities 108, could bearranged such that the signal S1 could be applied to an optionalconductive layer 116A that extends over the top of the HC cavities.Other variations are also possible in the gas feed geometry, since twoseparate gases 128, 140 are supplied to the wafer processing region 106at substantially alternating points over the array.

The temperature control layer 122 can be actively cooled by thetemperature control system 122A. Cooling the temperature control layer122 will draw heat away from the HC cavities 108. By way of example, thetemperature control layer 122 can include a coolant passing through thetemperature control system 122A to carry the heat away from the upperelectrode 103 to an external heat dissipation system (not shown). Thetemperature control system 122A can include other systems and methods ofcontrolling the temperature of the upper electrode 103 as are well knownin the art. By way of example the temperature control system 122A caninclude heat sinking, thermoelectric cooling, heating, and any suitablecooling media.

In one example where the etchant gas is composed of C4F8 and O2, theC4F8 molecule dissociates to form a variety of smaller atoms andmolecules some of which are chemically reactive radicals. In particular,C2F4, C3F5, and other multicarbon species are partly responsible forpolymerization processes which passivate the mask, sidewall, and stoplayer through polymer deposition. In contrast, CF3 and F radical speciesact, in combination with ion bombardment, to etch the SiO2-based film tobe etched. O radicals are produced by dissociation of O2. O radicalsetch polymer, especially in combination with ion bombardment, thusallowing a controllable degree of net polymerization. By enabling alower degree of dissociation than the typical processes, the presentprocesses provide a greater ratio of passivant to etchant, which is morefavorable for selective etching.

With the above embodiments in mind, it should be understood that theinvention may employ various computer-implemented operations involvingdata stored in computer systems. These operations are those requiringphysical manipulation of physical quantities. Usually, though notnecessarily, these quantities take the form of electrical or magneticsignals capable of being stored, transferred, combined, compared, andotherwise manipulated. Further, the manipulations performed are oftenreferred to in terms, such as producing, identifying, determining, orcomparing.

The invention can also be embodied as computer readable code on acomputer readable medium. The computer readable medium is any datastorage device that can store data, which can thereafter be read by acomputer system. Examples of the computer readable medium include harddrives, network attached storage (NAS), read-only memory, random-accessmemory, CD-ROMs, CD-Rs, CD-RWs, DVDs, Flash, magnetic tapes, and otheroptical and non-optical data storage devices. The computer readablemedium can also be distributed over a network coupled computer systemsso that the computer readable code is stored and executed in adistributed fashion.

Any of the operations described herein that form part of the inventionare useful machine operations. The invention also relates to a device oran apparatus for performing these operations. The apparatus may bespecially constructed for the required purposes, or it may be ageneral-purpose computer selectively activated or configured by acomputer program stored in the computer. In particular, variousgeneral-purpose machines may be used with computer programs written inaccordance with the teachings herein, or it may be more convenient toconstruct a more specialized apparatus to perform the requiredoperations.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

What is claimed is:
 1. A method of etching a semiconductor wafercomprising: injecting a source gas mixture into a process chamberincluding: injecting the source gas mixture into a plurality of hollowcathode cavities in a top electrode of the process chamber; generating aplasma in each one of the plurality of hollow cathode cavities includingapplying a first biasing signal to the plurality of hollow cathodecavities; and outputting the generated plasma from corresponding outletsof each of the plurality of hollow cathode cavities into a waferprocessing region in the process chamber, the wafer processing regionbeing located between the outlets of each of the plurality of hollowcathode cavities and a surface to be etched; injecting a etchant gasmixture into the wafer processing region, the etchant gas mixture beinginjected through a plurality of injection ports in the top electrodesuch that the etchant gas mixture mixes with the plasma output from theoutlets of the plurality of hollow cathode cavities including generatinga desired chemical species in the wafer processing region and whereinthe etchant gas mixture is substantially prevented from flowing into theoutlets of each of the plurality of hollow cathode cavities by the gasand the plasma flowing from the outlets of each of the plurality ofhollow cathode cavities; and etching the surface to be etched.
 2. Themethod of claim 1, wherein generating plasma in each one of theplurality of hollow cathode cavities includes cooling the top electrode.3. The method of claim 1, wherein biasing the plurality of hollowcathode cavities includes applying the first biasing signal to a secondconductive layer of the top electrode, the plurality of hollow cathodecavities being formed in the second conductive layer.
 4. The method ofclaim 1, wherein the first biasing signal includes an RF biasing signal.5. The method of claim 1, wherein the first biasing signal including anRF signal within a range of between about 1 MHz and about 15 MHz.
 6. Themethod of claim 1, wherein the plurality of injection ports aresubstantially distributed across the wafer processing region surface ofthe top electrode.
 7. The method of claim 1, wherein the plurality ofhollow cathode cavities are substantially distributed across the waferprocessing region surface of the top electrode.
 8. The method of claim1, wherein the plurality of hollow cathode cavities and the plurality ofinjection ports are substantially evenly interspersed across the waferprocessing region surface of the top electrode.
 9. The method of claim1, wherein outputting the generated plasma from corresponding outlets ofeach of the plurality of hollow cathode cavities includes applying asecond biasing signal to the lower electrode.
 10. The method of claim 1,wherein generating plasma in each one of the plurality of hollow cathodecavities includes applying a third bias signal to the outlets of theplurality of hollow cathode cavities.
 11. The method of claim 1, whereingenerating plasma in each one of the plurality of hollow cathodecavities includes applying a third bias signal to the outlets of theplurality of hollow cathode cavities, the third bias signal being aground potential.
 12. The method of claim 1, wherein etching the surfaceto be etched includes removing etch byproducts from the wafer processingregion.
 13. The method of claim 1, further comprising applying a groundpotential to a first conductive layer of the top electrode.
 14. Themethod of claim 1, wherein the plurality of hollow cathode cavitiesinclude a plurality of hollow cathode trenches.
 15. The method of claim1, wherein plurality of injection ports in the top electrode include aplurality of injection trenches.
 16. The method of claim 1, wherein thesource gas mixture is an inert gas.
 17. The method of claim 1, whereinthe etchant gas mixture includes a fluorocarbon containing gas.
 18. Themethod of claim 1, wherein the outlet for each one of the plurality ofhollow cathode cavities has a width of greater than twice a plasmasheath thickness.
 19. A method of etching a semiconductor wafercomprising: injecting a source gas mixture into a process chamberincluding: injecting the source gas mixture into a plurality of hollowcathode cavities in a top electrode of the process chamber; generating aplasma in each one of the plurality of hollow cathode cavities includingapplying a first biasing signal to the plurality of hollow cathodecavities; producing activated species in the hollow cathode cavities;and outputting the produced activated species from corresponding outletsof each of the plurality of hollow cathode cavities into a waferprocessing region in the process chamber, the wafer processing regionbeing located between the outlets of each of the plurality of hollowcathode cavities and a surface to be etched; injecting an etchant gasmixture into the wafer processing region, the etchant gas mixture beinginjected through a plurality of injection ports in the top electrodesuch that the etchant gas mixture mixes with the activated speciesoutput from the outlets of the plurality of hollow cathode cavitiesincluding: generating a plasma in the wafer processing region; andgenerating a desired chemical species in the wafer processing region andwherein the etchant gas mixture is substantially prevented from flowinginto the outlets of each of the plurality of hollow cathode cavities bythe activated species flowing from the outlets of each of the pluralityof hollow cathode cavities, wherein the outlet for each one of theplurality of hollow cathode cavities as a width of less than twice aplasma sheath thickness; and etching the surface to be etched.